A review of a cold-atom clock based on coherent population trapping that highlights recent progress will be presented. Improvements in the coherence of the interrogation spectrum have resulted in the generation of dark states in the cold Rb atoms with essentially 100 % transmission – evidence that decoherence in this system is negligible. This improvement in coherence has resulted in improved short-term stability at the level of 1.5E-11 fractional frequency stability for a one second integration period. In combination with improved interrogation schemes, the improved spectrum has also resulted in dramatically smaller light shifts and improved long-term frequency stability – with the clock averaging down to the level of 1E-13 fractional frequency stability on time scales of over 10,000 seconds.

This paper describes a technique that allows measurement of very small alternating accelerations. It is based on a quantum version of a lock-in amplifier,1 which filters out spectral components far from the frequency of the measured signal, improving the signal-to-noise ratio of the measurement. As a proof-of-principle, a controlled experiment using microwave radiation is performed, modulating the phase of the control pulses at a given frequency. A strong response at twice the modulation frequency is observed as expected. Preliminary results of measurements taken with Raman control are also presented, in which a controlled modulation of the phase was obtained by modulating a piezoelectric actuator, causing one of the Raman mirrors to vibrate.

The present work presents a new method for enhancement of contrast of coherent population trapping resonance in Rb vapour based on feedback and fast digital processing of the error signal in the feedback loop. In the proposed method, when the frequency difference between the pump field components is detuned from the resonance of coherent population trapping, a linear combination of two measured values, — pump field power prior and after passing through the cell, — is stabilised. This parameter combination is stabilised through adjustment of the pump radiation power with an electrooptical amplitude modulator. The studied method is shown to improve CPT resonance contrast by more than two orders of magnitude, while also improving the signal-to-noise ratio more than two-fold. The possibilities and limitations of the proposed method for enhancement of CPT resonance contrast are analysed.

We demonstrate a significant improvement when referencing a frequency comb to an acetylene stabilized fiber laser as compared to a GPS-disciplined Rb clock reference. The Stabilaser 1542 is a compact, maintenance-free stand-alone acetylene stabilized fiber laser with a narrow linewidth and an Allan deviation of 3E-13 and 4E-14 in 1 s and 10000 s, respectively. Switching the comb reference from the Rb clock to the Stabilaser 1542 improves both comb linewidth and Allan deviation by about two orders of magnitude. Furthermore, long-term measurements of the Stabilaser 1542 frequency with reference to the GPS-disciplined clock indicate a potential accuracy of 1E-12.

Light pulse atom interferometry can be used to realize high-performance sensors of accelerations and rotations. In order to broaden the range of applications of these sensors, it is desirable to reduce their size and complexity. Point source interferometry (PSI) is a promising technique for accomplishing both of these goals. With PSI, rotations are measured by detecting the orientation and frequency of spatial fringe patterns in the atomic state. These spatial fringes are primarily due to a correlation between an atom's initial velocity and its final position, which is created by the expansion of a cold atom cloud. However, the fringe patterns are also influenced by the structure of the initial atomic distribution. We summarize several methods that can be used to investigate the relationship between the spatial fringe pattern and the initial atomic distribution. This relationship will need to be understood in detail to realize an accurate gyroscope based on PSI.

Since the pioneering work of Ramsey, atom interferometers are employed for precision metrology, in particular to measure time and to realize the second. In a classical interferometer, an ensemble of atoms is prepared in one of the two input states, whereas the second one is left empty. In this case, the vacuum noise restricts the precision of the interferometer to the standard quantum limit (SQL). Here, we propose and experimentally demonstrate a novel clock configuration that surpasses the SQL by squeezing the vacuum in the empty input state. We create a squeezed vacuum state containing an average of 0.75 atoms to improve the clock sensitivity of 10,000 atoms by 2.05 dB. The SQL poses a significant limitation for today's microwave fountain clocks, which serve as the main time reference. We evaluate the major technical limitations and challenges for devising a next generation of fountain clocks based on atomic squeezed vacuum.

Dynamic population Bragg gratings can be recorded in the rare-earth-doped (e.g. doped with erbium or ytterbium) optical fibers with mWatt-scale cw laser power. Two-wave mixing (TWM) via such gratings is utilized in single-frequency fiber lasers and in adaptive interferometric fiber sensors with automatic stabilization of the operation point. Slow and fast light propagation can also be observed in the vicinity of narrow (~20-200Hz) spectral profile of stationary no-degenerate TWM. In particular, slow light propagation is observed for the purely amplitude grating, recorded in the erbium-doped fiber in spectral range 1510-1550nm. In its turn, in ytterbium-doped fibers at 1064nm (or in erbium-doped fiber at the wavelength below 1500nm) the dynamic grating has significant contribution of the phase component, the TWM profile has essentially asymmetric form, and both slow and fast (superluminal) light propagation is possible at different frequency off-sets between the counter-propagating interacting waves.

Low-pressure acetylene in the hollow-core photonic crystal structure fibers is an excellent medium for the room-temperature investigation of the coherent quantum effects in communication wavelength region. Pulsed excitation enables observation of new coherent phenomena like optical nutation or photon echo and evaluation of important temporal characteristics of the light-molecule interactions. We also report original experimental results on the pulsed excitation of the electromagnetically induced transparency in co- and counter-propagation configurations.

We predict a new type of fast chirped soliton at a femtosecond pulse propagation in a medium containing the noble nanoparticles. This soliton type is characterized by the complicated pulse chirp. At our analysis we take into account the TPA of laser radiation by nanorods, and time-dependent nanorod aspect ratio changing due to their reshaping because of laser energy absorption. The chirped soliton is formed due to the trapping of laser radiation by the nanorods reshaping front, if a positive or negative phase-amplitude grating is induced by laser radiation. We analyze the conditions for the soliton with complicated chirp occurrence and numerically investigate their propagation.

We investigate the phase and group delay in eye-like ring resonator with the effect of different coupling coefficients and attenuation factors. The eye-like structure is composed of two bus waveguides coupling with the outer ring and the two rings coupling together which have the same perimeters. The eye-like ring resonator has two outputs which have different transmission characteristics. In this paper, we measure the group delay of the two outputs through changing the coupling coefficients and the attenuation factors of the inner and the outer ring. The result shows that the two outputs have reverse group delay (superluminal and slow light) which will have potential use in slow light fiber, optical buffers and optical switches.

We theoretically demonstrate the transmittion spectra and dispersion characteristics based on the electromagnetically induced transparency like effect in the nested fiber double-ring resonator with the transfer matrix theory; the system which are connected by three directional couplers consists of two inner rings, one outer ring and one straight waveguide. The simulation results show that the tunable group delay can be realized by changing the coupling coefficients. In the NDRR coupled Mach-Zehnder interferometer system, we obtained fast light and slow light simultaneously. By adjusting appropriate parameters, we can archive flat band group delay curve that has a profound application in optical interferometer, optical buffer, optical filter, optical modulator, dynamic or static optical sensing field.

The emerging field of on-chip integration of nanophotonic devices and cold atoms offers extremely strong and pure light-matter interaction schemes, which may have profound impact on quantum information science. In this context, a long-standing obstacle is to achieve strong interaction between single atoms and single photons, while at the same time trap atoms in vacuum at large separation distances from dielectric surfaces. In this work, we study new waveguide geometries that challenge these conflicting objectives. The designed photonic crystal waveguides are expected to offer a good compromise, which additionally allow for easy manipulation of atomic clouds around the structure.

We present a generalization of the input-output formalism that provides an analytic and systematic computation tool for few-photon scattering matrix in waveguide quantum electrodynamics (QED) systems. We also discuss the theoretical constraints on such scattering matrix from the cluster decomposition principle in quantum field theory.

Optically-pumped magnetometers have demonstrated magnetic field measurements as precise as the best superconducting quantum interference device magnetometers. Our group develops miniature alkali atom-based magnetic sensors using microfabrication technology. Our sensors do not require cryogenic cooling, and can be positioned very close to the sample, making these sensors an attractive option for development in the medical community. We will present our latest chip-scale optically-pumped gradiometer developed for array applications to image magnetic fields from the brain noninvasively. These developments should lead to improved spatial resolution, and potentially sensitive measurements in unshielded environments.

Recent developments in magnetic field sensing with negatively charged nitrogen-vacancy centers (NV) in diamond employ magnetic-field (MF) dependent features in the photoluminescence (PL) and eliminate the need for microwaves (MW). Here, we study two approaches towards improving the magnetometric sensitivity using the ground-state level anti-crossing (GSLAC) feature of the NV center at a background MF of 102.4 mT. Following the first approach, we investigate the feature parameters for precise alignment in a dilute diamond sample; the second approach extends the sensing protocol into absorption via detection of the GSLAC in the diamond transmission of a 1042nm laser beam. This leads to an increase of GSLAC contrast and results in a magnetometer with a sensitivity of 0.45 nT/√Hz and a photon shot-noise limited sensitivity of 12.2 pT/√Hz.

I discuss new ways to grow diamond that promise near-deterministic design of fluorescent color-centers, optimized for quantum sensing applications. Briefly diamonds are grown around diamond-like organic seed molecules that have the dopant atoms needed for specific color centers, located in the correct approximate locations. It can be seen that this approach can give unprecedented control over the number and placement of color centers. Complete quantum registers might also be fabricated, for example a nitrogen-vacancy and at 13C atom with a well-defined separation surrounded by only 12C diamond. In this talk I will discuss our first key success, which is growing diamonds under conditions where the seed molecules are stable, as well as current experiments.

In many experiments involving cold atoms, it is crucial to know the strength of the magnetic field and/or the magnetic field gradient at the precise location of a measurement. While auxiliary sensors can provide some of this information, the sensors are usually not perfectly co-located with the atoms and so can only provide an approximation to the magnetic field strength. In this article, we describe a technique to measure the magnetic field, based on Raman spectroscopy, using the same atomic fountain source that will be used in future magnetically sensitive measurements.

Slow light, i.e., the delay of an incident resonant pulse, can be observed in the throughput of an optical whisperinggallery microresonator. It can be produced by a single overcoupled whispering-gallery mode (WGM), or, more usefully, through induced transparency effects that are observed in the case of two coresonant WGMs with very different quality factors. There are several different methods for achieving induced transparency, two of which will be considered here. In addition, under the right conditions, light in a WGM can excite acoustic WGMs by forward Brillouin scattering. This nonlinear process due to electrostriction has a threshold, above which energy is transferred from the first optical WGM to the acoustic WGM and to a lower-frequency optical WGM. When one of the optical WGMs taking part in this optomechanical process is also involved in the production of slow light, the pulse delay can be affected. Analytical expressions for pulse delay in the three cases mentioned above are examined in terms of the WGM intracavity powers and it is shown that when the higher-frequency optical WGM is responsible for slow light, the pulse delay is reduced when the optomechanical process occurs. This conclusion is verified by a numerical model.

We demonstrate an inherently self-stable Brillouin fiber laser in telecom wavelengths, stemming from a natural thermal
feedback mechanism. Such lasers demonstrate great stability which significantly overcomes the hampering drift often
associated with fiber lasers.

Thermodynamic phase noise in passive fiber devices is generally so weak that in most devices, in particular fiber sensors, it has only been observed in fiber lengths in the range of 1 meter or much longer. Here we present a passive fiber strain sensor only 4.5 mm in length in which the noise in the frequency range of 1 kHz to ~12 kHz is limited by thermal phase noise in the fiber. The phase noise could be measured in such a short fiber by utilizing a slow-light fiber Bragg grating (FBG) resonator in which the phase noise is magnified by the resonator's slowing-down factor ng/n ≈ 370, where ng is the group index. At the same time, the usually dominant laser frequency noise was brought below the level of the phase noise by using a short fiber and a low-noise laser with a linewidth under 200 Hz. At 4 kHz, the total measured noise expressed in units of strain is 110 fε/√Hz, and the phase noise accounts for 77% of it. This sensor resolves a single-pass thermodynamic length fluctuation of only 5 x10-16 m/√Hz. These measurements provide experimental support for the dependencies of the phase noise on the fiber resonator length and group index predicted by a recent model.

We present a tunable delay line suitable for femtosecond pulse trains based on cascaded electrically-controlled nematic liquid crystal cells. Simple and collinear implementations enable to shape the achievable temporal range, with sub-femtosecond temporal accuracy, thus disclosing ultrafast applications in nematic liquid crystal-based devices. Independent control of the phase and group delay of femtosecond pulses is demonstrated. Furthermore, we successfully extend the method to Fourier-Transform hyperspectral imaging. The proposed devices are compact, low-cost, with no moving parts, scalable in size and spectral range.

In the talk we will discuss the role of disorder-induced losses on the threshold of line-defect photonic crystal lasers. Experiments reveal an optimum cavity length, on the order of 10 unit cells, where the laser threshold density attains a minimum. The results can be explained by considering the role of slow-light propagation on the threshold of a photonic crystal laser. We will also discuss the possibility of alleviating this dependence on cavity length by replacing one of the mirrors with a narrow-band mirror based on a Fano resonance.

Dynamical holography is an interferometric method that allows the measurements of phase modulations in the presence of environmental low-frequency fluctuations. The technique is based on the use of a nonlinear recombining medium that performs the dynamic hologram through a beam-coupling process. In our work, as the nonlinear medium, we use an optically addressed spatial light modulator operating at 1:55 μm. The beam coupling process allows obtaining a phase modulation sensitivity of 200 μrad= √Hz at 1 kHz. The interferometer behaves as an optical high pass filter, with a cutoff frequency of approximately 10 Hz, thus, filtering slow phase disturbances, such as due to temperature variations or low frequency fluctuations, and keeping the detection linear without the need of heterodyne or active stabilization. Moreover, owing to the basic principles of holography, the technique can be used with complex wavefronts, such as the speckled field reflected by a highly scattering surface or the optical field at the output of a multimode optical fiber. We demonstrate, both theoretically and experimentally, that using a multimode optical fiber as sensing element, rather than a single mode fiber, allows improving the interferometer phase sensitivity. Finally, we present a phase-OTDR optical fiber sensor architecture using the adaptive holographic interferometer.

unlimited number of equal copies of the signal spectrum is generated. Electrical sampling instead produces a limited number of copies multiplied by a sinc-function. All-optical sampling can be seen as the multiplication of the copies by a Gaussian function. Here we present a very simple method of all-optical sampling which requires neither nonlinear optics nor a mode-locked laser. Besides practical limitations, the only difference to ideal sampling is the fact that a limited number of copies is generated. The idea behind the method as well as first preliminary results for sampling rates up to 90 GSa/s are presented.